1. Field of the Invention
This invention relates to the treatment of apertured plates with a gas. More specifically the invention has been developed for the treatment of apertured thin steel plates with a nitriding or nitrocarburising gaseous medium to form a layer of iron nitride on the surfaces of the plates. The invention provides apparatus for such treatment, a method of treatment and a fixture on which a multiplicity of plates can be supported for treatment.
2. Description of the Prior Art
It is known from U.S. Pat. No. 4,793,871 assigned to Lucas Industries plc and issued Dec. 27th 1988 to treat steel plates to provide an iron nitride layer thereon by heating the plates in an inert atmosphere in a retort and then evacuating the inert atmosphere and introducing a nitrogen-containing gas which reacts with the heated plates to form the iron nitride layer on the surface thereof.
In prior apparatus used for this purpose, the number of plates that could be accommodated in the retort so as to be properly treated was limited since one relied solely on the undirected circulation of the nitrogen-containing gas through the furnace by a fan.